Friday, it is expected that various people will return to the Potomak River as 67 people in the United States killed 67 people in almost a quarter of the century.

Investigators have already recovered a roof recorder of the American airline, which collided with the army helicopter, as the plane landed at Ronald Reagan National Airport, Nez.

All of the two plane were killed, and the helicopter was apparently the operations of air traffic control, as well as the control of air traffic. Officials do not speculate on many agencies involved in the exam on Thursday.

The authorities were still looking for a recorder of the Student Council-60 BAZ helicopter, and Defense Minister Pete said on Friday. As a result of the accident, other factors, including the height of the helicopter and whether the staff used his night vision glasses, is still in the investigation.

More than 40 bodys of water have been dragged, law enforcement agencies told the Associated Press. Officials were not authorized to discuss the details of the investigation and talk about the state of anonymity.

Watch Like the events happened on Wednesday evening crash.

DC plane crash minute by minute

The National Assembly demolishes 5342 flights of American Airlines and the American Army Black Hawk Hawkk Hawk Hawk Hawk at Ronald Reagan Washington National Airport.

Air Traffic Supervisor Staff Exam

The plane took 60 passengers and four staff members, and under three soldiers was under a helicopter. One air traffic control was responsible for coordinating the helicopter and arriving planes and departure planes when the clash took place by the US Federal Aviation Management, which was purchased by the Associated Press.

These responsibilities are often divided between two people, but the airport usually combines roles in the evening. 30 on when the traffic begins to slow down. Wednesday the head of the tower routed them to be combined earlier.

“The position of the position was not normal for the day of the day and the volume of traffic,” the report said.

Positions are regularly combined when the controllers must leave the shutdown cylinder during changes or when air traffic is slow.

FAA has long been struggling with the lack of air traffic controllers.

Officials say that the conditions for flight are clear because the plane has arrived from the city of Wichita.

“The two pilots had flown this special route at night. That was not something new for anyone, “said Jonathan Kozol, Chief of Army Aviation Staff. The maximum allowable height of the helicopter was once 60 meters, said Kozoliol.

It was not clear immediately, it exceeded that limit.

Air area around Regan National can challenge even the most experienced pilots, no matter how ideal conditions. They have to navigate hundreds of other commercial planes, military planes and limited areas around sensitive sites.

Only 24 hours before the Fatal Clashes, various regional aircraft should have taken by the second opportunity to land in the national city of Reagan at the time when the military helicopter was reported nearby.

Watch L Explain the challenges in DC-Area Airspace.

DC plane crash. The complications of landing in Washington

Aviation experts say that landing at three large airports in Washington has been challenged for decades due to a high flight, limited airspace and two flying zones.

Data search can be a long process

Investigations of air crash can take several months, and experts warn that no two probes are the same, flight records are not always able to provide full responses. In fact, all accidents include many factors.

Two recorders are mandatory in civil aviation. Pilot sound recorder (CVR) for pilots' sounds or rooster sounds and a separate flight recorder (FDR). Some devices combine both functions.

After communicating with water, they must first dry dry and the data cleared ties are not randomly deleted. Audio and data files are downloaded and copied.

The data itself means less than a little. It should be deciphered from raw files before turning charts and other data synchronization, such as air traffic control transfers.

Laboratory experts sometimes use “spectral analysis”, deciphering flight sounds or decaying barely audible alarms.

In the 90s, a porridge in crashes, in which the recorders had stopped working when the government was lost, NTSB offers to provide a sufficient copy force.

Wednesday crash was the earliest in the United States in 2001. Since November 12, when the American airline flight came after leaving the Kennedy airport in the residential area of ​​Belly.

The latest major fatal accident involved in the US Commercial Airlines took place in 2009.

Experts often emphasize that the plane's journey is super-safe.